Electrically heated transparent panel

ABSTRACT

An electrically heated transparent panel is described for a laminated safety glass window construction having a clear polymer inner layer with a pattern of wrinkled resistance wires oriented in a three-dimensional non-parallel random fashion so as to reduce glare from the wires when the window is used in automative and other type vehicles. The individual resistance wires are partially embedded in the polymer sheet by a technique utilizing shrinkage of a thermoplastic polymer from its original dimensions when heated to an elevated temperature together with having the individual wires change configuration when relaxed from tension forces on the wire when first assembled with the polymer sheet. An improved form of bus-bar electrode means are connected at each end of the individual resistance wires by heat-bonding directly to the thermoplastic polymer sheet to provide the composite panel which can thereafter be handled and assembled by conventional further heat-bonding as the inner layer of a laminated safety glass construction.

United States Patent 1 Gruss 1 3,745,309 [451 July 10,1973

[54] ELECTRICALLY HEATED TRANSPARENT PANEL [75] Inventor: George A.Gruss, Mentor, Ohio [73] Assignee: General Electric Company,

Schenectady, NY.

[22] Filed: Oct. 31, 1972 [21] Appl. No.: 302,501

[52] US. Cl 219/522, 219/203, 219/541, 219/544 [51] Int. Cl. 1105b 3/06[58] Field of Search 219/203, 522, 541, 219/544; 29/611 [5 6] ReferencesCited UNITED STATES PATENTS 3,383,762 5/1968 Leclercg 29/611 3,378,9194/1968 Brittan 29/611 3,409,759 11/1968 Boicey et a1. 219/522 3,414,71312/1968 Reifeiss et al.... 219/522 3,484,584 12/1969 Shaw, Jr. 219/5223,601,583 8/1971 Fujiwara 219/522 FOREIGN PATENTS OR APPLICATIONS164,435 5/1921 Great Britain 219/522 462,641 10/1968 Switzerland 219/5221,288,186 2/1962 France 219/522 1,912,667 9/1970 Germany 219/522 PrimaryExaminerVolodymyr Y. Mayewsky Att0rneyJohn F. McDevitt et al.

[5 7] ABSTRACT An electrically heated transparent panel is described fora laminated safety glass window construction having a clear polymerinner layer with a pattern of wrinkled resistance wires oriented in athree-dimensional non-parallel random fashion so as to reduce glare fromthe wires when the window is used in automative and other type vehicles.The individual resistance wires are partially embedded in the polymersheet by a technique utilizing shrinkage of a thermoplastic polymer fromits original dimensions when heated to an elevated temperature togetherwith having the individual wires change configuration when relaxed fromtension forces on the wire when first assembled with the polymer sheet.An improved form of bus-bar electrode means are connected at each end ofthe individual resistance wires by heat-bonding directly to thethermoplastic polymer sheet to provide the composite panel which canthereafter be handled and assembled by conventional further heat-bondingas the inner layer of a laminated safety glass construction.

4 Claims, 3 Drawing Figures ELECTRICALLY HEATED TRANSPARENT PANELBACKGROUND OF THE INVENTION This invention relates generally to a safetyglass window construction which is generally suitable for heatingvehicle windows including the windshield, side and rear windows. Moreparticularly, it relates to a glass sandwich having an electricallyconducting transparent panel for the inner layer which is substantiallyfree from glare when light is transmitted through the safety glasswindow. Specifically, it relates to an electrically conductingtransparent panel for a safety glass window construction havingparticular bus-bar electrode means as part of a thermoplastic innerlayer along with a protruding array of resistance wires which enablessimplified and more reliable assembly of the final window constructionalong with improved heating of the window. I

In a pending U.S. Pat. application entitled, ELEC- TRICALLY HEATEDWINDOW, Ser. No. 166,064, filed July 26, 1971 in the names of George A.Gruss, George J. Polanka, and Leslie H. Pfeiler, which is assigned tothe assignee of the present invention, there is disclosed and claimed acomposite sheet member which comprises a layer of transparentthermoplastic polymer that has been heat-shrunk from its originaldimensions by heating to an elevated temperature having partiallyembedded in one major surface a plurality of wrinkled resistance wireswhich lie in closely spaced relationship and are oriented with respectto one another in non-parallel random fashion so that portions of saidindividual resistance wires protrude from said major surface of thethermoplastic polymer layer and form a three-dimensional heating wireconstruction with improved fabrication and operational advantages. Asone embodiment of said novel transparent heating panel which forms theotherwise conventional inner layer for a laminated safety glass windowconstruction, there is also described in said earlier filed applicationcertain bus-bar electrode means consisting of a single strip ofelectrically conducting material secured at each end of the individualresistance wires to form a parallelconnected electrical circuittherebetween. The single strip electrodes are in direct physical contactwith protruding portions of the individual resistance wires and providea generally reliable termination which is not subject to mechanicalrupture of the heating wires at the electrical terminations. On theother hand, these single bus-bar strips are secured by heat-bondingdirectly to one major surface of the thermoplastic polymer sheet withthe individual resistance wires being secured to the opposing side ofthe strips. Such termination can result in occasional failure of directelectrical contact between the strips and the heating wires which iscaused by excessive flow of the polymer material when the final windowassembly is made. Even without excessive flow of the plastic material,there can be increased contact resistance from chemical reaction betweenthe copper bus-bars and the plastic material after the final assemblyhas been put into use.

In said earlier filed application referenced above, there are alsodisclosed methods and apparatus for assembling the electrically heatedtransparent panel as Well as the final safety glass window assembly. Inone method of fabricating the electrically heated transparent panel, theelectrical resistance wire forming the heating wire pattern isprestressed to provide wrinkles when the resistance wire is not undertension. The prestressed wire is thereafter applied under tension to onemajor surface of the transparent thermoplastic polymer sheet in apattern having closely spaced parallel orientation with respect to theindividual wires whereupon the tension on the individual resistancewires is relaxed while retaining physical contact between the pattern ofresistance wires and the surface of the thermoplastic polymer sheet.During the subsequent heating step, the polymer sheet as well as thewires can expand and contract along the direction of the wire path. Thecomposite member is then heated by applying electrical power to theindividual resistance wires so that portions of the wires which are inphysical contact with the surface of the polymer sheet become embeddedand the remaining portions of the individual wires protrude from themajor surface of the plastic sheet. The composite member having abus-bar electrode configuration and the resistance wire pattern as abovedescribed can thereafter be assembled as the inner layer of an otherwiseconventional safety glass window construction in a variety of alreadyknown methods. The final heat-bonding step which produces the glasslaminate is also generally carried out under sufficient heating andcompressional forces that significant flow of the polymer materialoccurs.

A particular apparatus to fabricate the composite member is alsodescribed in said copending application which utilizes a collapsibledrum member upon which the member is formed. In so doing, thethermoplastic polymer sheet is first wrapped upon the drum followed byapplication of separate heating and bus-bar electrodes, and thenfollowed by winding of pi'estressed resistance wire in the form of ahelical coil over the wound polymer sheet. The composite member is thenformed by collapsing the drum a predetermined decrease in diameter andthereafter thermally tacking or heat-bonding the resistance wire and thesubjacent sin? gle element bus-bar electrodes to the polymer sheet.

The products and methods of the present invention constituteimprovements over said earlier disclosure which can utilize the samegeneral apparatus to assemble the electrically heated transparent panelof the present invention. Consequently, a detailed description of thesame apparatus need not be repeated in the pres ent specification exceptto explain the method of carrying out the present invention.

SUMMARY OF THE PRESENT INVENTION This invention provides a noveltechnique for incorporating improved bus-bar electrode means in anelectrically heated transparent panel of a laminated safety glassconstruction. The overall construction provides a laminated safety glassmember with improved ability to remove ice and snow as well as defrost.

The object of the present invention, therefore, is to provide a superiorelectrically heated safety glass construction including improved methodsto form the electrically heated transparent panel. Still a furtherobject is to provide an electrically heated laminated windowconstruction having improved thermal capacity for defrosting as well asremoving ice and snow from a windshield wherein the electrically heatedtransparent panel enables a simplified and more reliable assembly of thefinal glass laminate along with improved heating of the window. Stillanother object of the present invention is to provide simple andreliable means of assembling resistance wires with a thermoplasticpolymer sheet so that the composite member can be easily handledthereafter to produce a laminated safety glass member by conventionaltechniques.

Briefly stated, the improved bus-bar electrode means of the presentinvention which are connected at each end of the individual resistancewires to provide a parallel-connected electrical circuit therebetweeneach consists of a thin foil strip of electrically conducting metalhaving a segmented construction which is secured by heat-bondingdirectly to the thermoplastic polymer layer and a continuous foil stripof greater width and thickness than said segmented foil strip whichoverlays the subjacent segmented foil strip and is also heat-bondeddirectly to the thermoplastic layer. The individual resistance wires arejuxtapositioned at each end between the foil strips such that there isdirect physical and electrical contact between the continuous foil stripand the subjacent segmented strip. The subjacent segmented foil stripsare further heat-bonded to the thermoplastic polymer sheet in the finalglass laminate so as to deform and partially envelop the exteriorsurface portion of the individual resistance wires which improves theelectrical path to the overlying principal electrode strips of bus-bars.In this manner of construction, the subjacent segmented strips alsoserve as a barrier to plastic flow of the polymer sheet material whenthe final glass laminate is formed by heat-bonding under pressure whichotherwise could retard or interrupt the electrical path. Finally, thesegmented construction of the subjacent foil elements provide uniformthermal tacking of the resistance wires to the thermoplastic polymersheet when practicing the present invention as will be explained laterin more detail.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of acurved window member having a laminated safety glass constructionaccording to the present invention;

FIG. 2 is a section 2-2 along one longitudinal marginal edge of thewindow construction shown in FIG. 1;

' and FIG. is a section 3-3 taken through a different marginal edge ofthe same window construction.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention providessimple and effective means to reduce a major difficulty encountered witha parallel arrangement of resistance heating wires in a laminated safetyglass window. While the glare phenomena encountered is not fullyunderstood at the present time, it is believed attributable to the wiredirection rather than spacing between the individual ing athree-dimensional degree of spatial orientation is sufficient tosubstantially eliminate the glare problem.

Controlled randomization of the resistance wire pattern is obtained byapplying prestressed resistance wires upon one major surface of thesheet of transpar' ent thermoplastic material and thereafter utilizingthe ability of the polymer material to shrink from its originaldimensions when heated to elevated temperatures sufficient to embedportions of the individual wires in the contacted surface ofthermoplastic material. More particularly, a pattern of the prestressedresistance wires is applied under tension to one major surface of thethermoplastic sheet so that individual wires are in closely spacedparallel relationship in the composite member so formed which is thenheated under conditions permitting the individual resistance wires toexpand and adopt a'configuration attributable to the prestressed forces.Subsequent cooling of the composite member allows the wires to becomepartially embedded in the softened thermoplastic material and providesthe final randomization in the wire pattern such that individual wireshave a wrinkled or irregular crimp at irregular intervals along theirlength. A non-parallel relationship between adjacent wires is therebyformed with portions of the wire protruding from the surface of thethermopolymer layer at different elevations where not embedded. Thefinal non-parallel wire pattern will be governed by thermal expansiondifferences between the polymer sheet and the wire, the nature andextent of prestressed forces applied to the resistance wire beforeincorporation in the polymer surface, and the heat shrinkagecharacteristics of the thermoplastic material. It has also been notedduring experience with this mode of fabrication that certain polyvinylbutyral The relatively high heating capacity of the wire pat- I ternobtained inthe foregoing manner is due to using fine wire having adiameter from approximately 0.0003 to 0.0009 inches in a spacing from 10to 30 wires per inch. Since it will be recognized that wattagedissipation which can be obtained by connecting the wire pattern to asource of electrical energy will depend upon contact resistance as wellas other factors, it becomes desirable to provide an effective andefficient means of connecting the wire pattern to the electrical powersupply. Toward this end and as a principal feature of the presentinvention, the applicant has discovered novel bus-bar electrode meansfor connecting the wire pattern at each end of the individual resistancewires as an integral part of the electrically heated transparent panel.Said novel bus-bar electrode means along with its method of constructionwill now be described in connection with the drawings which accompanythis specification.

Turning now to the drawings, FIG. 1 represents a schematic view of anotherwise conventional automobile windshield having a curved contour andwhich includes the substantially glare-free resistance wire patternproduced in accordance with the present invention. More particularly, alaminated safety glass sandwich 10 is shown which comprises a pair ofouter glass layers 12 and 14 which are adhesively held together byheat-bonding to the electrically heated transparent each end of theindividual resistance wires to provide an electrical termination meansfor heating the wires from the available electric power supply in thevehicle. Both bus-bar members are disposed longitudinally over most ofthe longitudinal dimension of the window construction and are locatedboth proximate as well as parallel to opposing marginal edges 26 and 28of the curved safety glass window construction. In the FIG. 1 embodimentthe resistance wire pattern 20 is aligned transversely for electricaland physical contact at each end of the individual resistance wires sothat sections 30 and 32 of the wire pattern which lie beyond the extremeends of the longitudinal busbar direction are not part of the electricalheating system.

In FIG. 2, there is shown a vertical section through the windshieldconstruction of FIG. 1 to more clearly illustrate the bus-bar electrodeconfiguration of the present invention. While the degree ofthreedimensional resistance wire randomization which exists when theelectrically heated transparent panel is constructed according to theinvention is somewhat obscured in FIG. 2 by reason of the compressionforces applied during assembly of the final safety glass windowconstruction, there can still be seen portions 34 and 36 of anindividual resistance wire protruding from major polymer surface 38 ofthe thermoplastic polymer sheet. Thus, it can be seen that portions ofthe individual resistance wires which protrude at different elevationsfrom the polymer sheet surface are free to move when compressed by theadjacent glass layers during pressure lamination of the final glasssandwich using the present electrically heated transparent panel. In sodoing, the individual resistance wires undergo further randomorientation with respect to the plane of said major polymer sheetsurface in the final heat-bonding under pressure. In this manner offabricating the final window assembly it will'also be apparent that thethermoplastic polymer is relatively free to move during the finalheatbonding step and could interfere with the proper electricaltermination of the individual resistance wires unless means were adaptedto prevent such action.

As can be seen in FIG. 2 taken together with reference to FIG. 1, thebus-bar electrode configuration 22 in the final glass laminate consistsof a thin foil strip 40 having a segmented construction illustrated byslits 43,44, and 46 which is secured by heat-bonding to the underlyingthennoplastic layer and a continuous foil strip 42 of greater width andthickness which overlies the subjacent segmented strip and is alsoheat-bonded directly to the thermoplastic layer. The slit openings whichextend entirely through the segmented strip 40 provide an interruptedelectrically conducting path when the individual resistance wires arethermally tacked to the thermoplastic polymer sheet in a manner to beexplained in more detail hereinafter. The continuous foil strip is indirect contact on one side with the inner surface of glass outer layer12 while being In physical and electrical contact on the other side w=thboth an individual heating wire 20 and the subjacent segmented strip 40.The direct contact between the foil strips which can both be constructedof an electrically conducting metal such as copper is achieved throughpartial deformation of the underlying segmented strip which occurs bothduring thermal tacking of the individual resistance wires to thethermoplastic polymer sheet and the final window assembly in a manneralso to be further explained. The section in FIG. 2 was also chosen toillustrate a tab feature 48 of the continuous foil strip 42 whichpermits electrical connection to the vehicle power supply for the windowheating system.

FIG. 3 is a cross sectional view in the opposite direction of thebus-bar electrode means of the present invention. More particularly,asection 33 has been taken through laminated glass window member in adirection perpendicular to section 22 which is shown in FIG. 2 in orderto more clearly depict the final assembled configuration of anindividual bus-barelectrode. Thus, a laminated safety glass constructionis shown having the glass outer layers 12 and 14 integrally bondedtogether. with the electrically heated transparent panel 16 wherein theindividual resistance wires illustrated at 50, 52, and 54 which make upthe heating pattern 20 are positioned between the continuous foil strip42 and the subjacent segmented strip 40. As can be noted, the subjacentsegmented strip has been partially deformed to envelop the exteriorsurface of. the individual resistance wires in accordance with apreferred method of fabricating the electrically transparent panelhavingsuch bus-bar electrode means as an integral part. It should alsobe noted in said bus-bar configuration that portions of the segmentedstrip which do not envelop the individual resistance wires are in directphysical and electrical contact with the overlying continuous strip 42.

A preferred method of fabricating the electrically heated transparentpanel having a three-dimensional non-parallel random configuration ofresistance wires along with the bus-bar electrode members of the presentinvention utilizes the general process described and claimed in theaforementioned pending'patent application. Hence, the general processwhich forms no part of the present invention need not again be describedin the present specification except in relation to applying the improvedbus-barmeans to the electrically heated transparent panel. Accordingly,a pair of the segmented foil strips are first applied upon one majorsurface of the sheet of transparent thermoplastic polymer which shrinksfrom its original dimensions when heated to an elevated temperature sothat each strip is located proximate and parallel to an opposingmarginal edge of the contour defining a curved safety glass windowmember. Thereafter, a transverse pattern of the resistance wires isapplied in parallel orientation with respect to one another between saidsegmented foil strips and so that said wire pattern extends beyond thesegmented strip. This step is followed by securing the wire pattern tothe same major surface of the polymer sheet using electrical heatingelectrodes placed at the end of the individual resistance wiresaccording to the known process. Electrical power can then be applied tothe heating electrodes so that the polymer sheet and resistance wirescan expand and contract during heating to embed portions of the wires inthe surface of the polymer sheet also in accordance with the knownprocess. The foil strips are segmented in order to apply electricalpower uniformly with the heating electrodes since the curved contour ofthe window and the conforming wire pattern provide individual resistancewires of unequal length which would otherwise be subject to nonuniformheating. The segmented fo il strips undergo slight deformation duringthis thermal tacking step sufficient for partial contact with thesubsequent applied continuous foil strips wires and further provide abarrier layer at the electrical terminations to any flow ofthermoplastic polymer material during the final heatbonding step of thewindow assembly. The continuous foil strips 42 of sufficient width andthickness to satisfy the electrical current carrying requirements andenable direct bonding to the same major surface of the polymer sheet arenext secured by supplemental thermal tacking which can take place afterremoval of the heating electrodes. The customary final heat-bonding stepused in production of the glass laminate provides further deformation ofthe segmented foil strips wherein said strips envelop the exteriorsurface portion of the individual resistance wires resulting in directphysical and electrical contact with the overlying continuous foilstrips.

The above described method of forming the improved bus-bar electrodemeans of the present invention can be carried out upon the sameapparatus described and claimed in the aforementioned copendingapplication. More particularly, said known apparatus employs acollapsible drum member which cooperates with mechanical means ofprestressing the resistance wires to obtain the wrinkled resistance wireconfiguration. This is accomplished by applying a transverse pattern ofthe prestressed resistance wire under tension between the segmented foilstrips prior to thermal tacking of the resistance wires on thethermoplastic polymer sheet. In the present method of applying thebusbar electrodes, the collapsible drum member of said known apparatuscan be supplied with template means defining the curved window contour.For example, a template pattern for the window of FIG. 1 would bealigned with its longitudinal dimension in the direction of thelongitudinal drum axis. Said template means can simplybe a scribedoutline located on the periphery of the drum surface over which thesheet of the thermoplastic transparent polymer is wrapped. In employingsuch modified apparatus to fabricate the electrically heated transparentpanel, the segmented foil strips are applied on the outer surface of thewrapped polymer sheet so that each strip is located proximate andparallel to an opposing marginal edge of the curved glass window memberat the locations fixed by the template means. A helical coil of theresistance 'wire is next wound about the drum periphery which is thensecured to the outer surface of the polymer sheet and with the heatingelectrodes being next located externally of the window area. As a moredetailed explanation of carrying out the present method with said knownapparatus, the process of forming the electrically heated transparentpanel includes the following steps:

a. applying the segmented foil strips upon the outer surface of thethermoplastic polymer sheet so that each strip is located proximate andparallel to an opposing marginal edge of the curved safety glass windowmember,

b. prestressing the resistance wire to provide wrinkles therein when theresistance wire is not under tension,

applying a transverse pattern of the prestressed wire under tensionbetween the segmented foil strip so that the wire pattern extends beyondthe strips and securing the wire pattern to the collapsible drumperiphery with heating electrodes located externally of the window area,

(1. relaxing tension upon the resistance wires while retaining physicalcontact between the pattern of resistance wires and the surface ofthermoplastic polymer so that the polymer sheet can contract along thedirection of the wire path,

e. supplying electrical power to the heating electrodes sufficient toembed those portions of the wire in physical contact with the surface ofthe polymer sheet, and

f. securing the continuous foil strips by heat-bonding to the same majorsurface of the polymer sheet for direct contact with the individualresistance wires and the subjacent segmented foil strips.

It will be noted in the above method that the foil strips are alignedalong the longitudinal marginal edges of the curved safety glass. memberand as earlier stated, the continuous foil strips can be applied by asupplemental thermal tacking step after the electrically transparentpanel has been removed from the drum periphery by heating means otherthan the heating electrodes. After securing the continuous foil stripsto complete the busbar electrode means of the present invention, theheating panel can thereafter be easily handled to produce a laminatedsafety glass member in the conventional manner.

Specific operation of the known apparatus to form such electricallyheated transparent panel would include the following essential steps:

a. wrapping a sheet of transparent thermoplastic polymer around thecircumference of the collaps ible drum and fixing both ends of the sheetto the drum, i

b. applying a pair of segmented foil strips to the outer surface of thepolymer sheet at locations proximate and parallel to opposing marginaledges of the curved safety glass .window contour,

c. winding a helical coil of prestressed resistance wires in closelyspaced relationship upon the drum periphery in contact with the outersurface of the secured polymer sheet and maintaining tension uponeachtum of the resistance wires,

(1. securing the wire coil to the outer surface of the polymer sheetwith heating electrodes located between the segmented foil strips andnot in the area of the window member,

e. collapsing the drum by predetermined decrease in diameter,

f. supplying electrical power to the heating electrodes sufficient toembed portions of the wire in the surface of the polymer sheet, and

g. applying the continuous foil strips for direct contact with theindividual resistance wires and the subjacent segmented foil strips toprovide the final bus-bar electrode.

It can be appreciated in the foregoing method that reduction of the drumcircumference permits the composite member to sag under gravitationalforces from the drum surface which relaxes the tension forces on theresistance wire thereby enabling it to crimp or wrinkle along its lengthwhile still maintaining point contact with the polymer sheet. Whenelectrical energy is supplied by means of the heating electrodes to thewire pattern while in this sagged configuration, the polymer material isheated to its softening point, thereby permitting portions of the wirestill in physical contact with the polymer surface to become embeddedtherein. Under these heating conditions, both polymer sheet and wirepattern are permitted to expand and contract along the direction of thewire pattern depending upon the individual thermal expansioncharacteristics while still remaining in physical contact. It has alsobeen noted during this heating operation that the polymer sheetcontracts visibly while still being heated after first undergoingthermal expansion perpendicular to the direction of the wire path. Whenheating is discontinued by interrupting the electrical energy beingsupplied to the wire pattern after the shrinkage has taken place and thecomposite member then allowed to cool, there is produced an adhesivebond at the embedded portions of the wire pattern. By further reason ofalignment between the wire path and the shrinkage direction of thepolymer sheet, it can be seen that a greater randomization in the finalwire pattern as provided than otherwise would occur.

It can be appreciated in the foregoing description of preferredembodiments that other methods could be employed to provide an improvedbus-bar electrode configuration with comparable results. Likewise, it isalso contemplated to employ the methods herein disclosed in providingthe same type bus-bar configuration for different heating wire patternsin a safety glass window member. As one example, the bus-bar electrodescould be oriented in a transverse direction of the window member withthe heating wire pattern extending in the longitudinal direction.Additionally, the present bus-bar configuration could be employed with anonrandom parallel array of the heating wire to provide certain of thesame benefits discovered by the applicant. It is intended to limit thepresent invention, therefore,'only the scope of the following claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In a laminated safety glass member which comprises a pair of glassouter layers having a composite inner layer integrally bonded thereto,said composite inner layer comprising a sheet of transparentthermoplastic polymer which has been heat shrunk from its originaldimensions by heating to an elevated temperature having partiallyembedded in one major surface a plurality of wrinkled resistance wireswhich lie in closely spaced relationship and are oriented with respectto one another in non-parallel random fashion so that portions of saidindividual resistance wires protrude from said major surface of thethermoplastic polymer layer, and bus-bar electrode means connected ateach end of the individual resistance wires, the improvement whereinsaid bus-bar electrode means consist of a thin foil strip having asegmented construction which is secured by heat-bonding directly to thethermoplastic polymer layer at each end of the individual resistancewires with a continuous foil strip of greater width and thickness whichoverlays the subjacent segmented strip and is also heat-bonded directlyto the thermoplastic polymer layer at each end of said individualresistance wires.

2. A laminated safety glass member as in claim 1 wherein the continuousfoil strip is in direct contact with the inner surface of one glassouterlayer and the individual resistance wires are positioned betweensaid continuous foil strip and the subjacent segmented strip.

3. A laminated safety glass member as in claim 1 wherein the continuousfoil strip is in direct physical contact with both resistance wires andthe subjacent segmented strip.

4. A laminated safety glass member as in claim 1 wherein the continuousfoil strip is in direct contact with the inner surface of one glassouterlayer, the individual resistance wires are positioned between saidcontinuous foil stripand the subjacent segmented strip which has beenpartially deformed by heat-bonding to envelop the exterior surfaceportion of said individual resistance wires, and the opposite majorsurface of the thermoplastic polymer layer is heat-bonded to the innersurface of the other glass outerlayer.

1. In a laminated safety glass member which comprises a pair of glassouter layers having a composite inner layer integrally bonded thereto,said composite inner layer comprising a sheet of transparentthermoplastic polymer which has been heat shrunk from its originaldimensions by heating to an elevated temperature having partiallyembedded in one major surface a plurality of wrinkled resistance wireswhich lie in closely spaced relationshIp and are oriented with respectto one another in nonparallel random fashion so that portions of saidindividual resistance wires protrude from said major surface of thethermoplastic polymer layer, and bus-bar electrode means connected ateach end of the individual resistance wires, the improvement whereinsaid bus-bar electrode means consist of a thin foil strip having asegmented construction which is secured by heat-bonding directly to thethermoplastic polymer layer at each end of the individual resistancewires with a continuous foil strip of greater width and thickness whichoverlays the subjacent segmented strip and is also heat-bonded directlyto the thermoplastic polymer layer at each end of said individualresistance wires.
 2. A laminated safety glass member as in claim 1wherein the continuous foil strip is in direct contact with the innersurface of one glass outerlayer and the individual resistance wires arepositioned between said continuous foil strip and the subjacentsegmented strip.
 3. A laminated safety glass member as in claim 1wherein the continuous foil strip is in direct physical contact withboth resistance wires and the subjacent segmented strip.
 4. A laminatedsafety glass member as in claim 1 wherein the continuous foil strip isin direct contact with the inner surface of one glass outerlayer, theindividual resistance wires are positioned between said continuous foilstrip and the subjacent segmented strip which has been partiallydeformed by heat-bonding to envelop the exterior surface portion of saidindividual resistance wires, and the opposite major surface of thethermoplastic polymer layer is heat-bonded to the inner surface of theother glass outerlayer.